Astronomers can use such phenomena as the spectral shift of light coming from distant galaxies to infer that the universe is expanding out of a very small volume about 15 billion years ago. Some physicists have proposed that volume was the size of the solar system or less, maybe even the size of a dime. As the universe expanded from a state of pure energy, hydrogen atoms evolved through a process called nucleosynthesis. Later, hydrogen gas clouds condensed to form main sequence stars. Fusion of hydrogen within the stars lead to the formation of helium. When stars the size of our sun (i.e., stars with one solar mass) burned toward extinction after about 10 billion years, their center collapsed while the outer gas layers expanded to form a red giant. The pressure and temperature in the center of a red giant was large enough to allow the fusion of alpha particles (i.e., helium without electrons) to form heavier elements including oxygen, and carbon. Note that an alpha particle has two protons and two neutrons so that the major products of fusion all had even atomic weights (i.e., an even number of protons). Pressure and temperature were not large enough in the red giants to produce the heavier elements.

On rare occasions a star would form with more than 20 times the mass of our sun. These stars would burn faster and collapse with the outer gas cloud expanding into a super red giant. The pressure in the center of these super stars was high enough to produce the heavier elements including silicon, magnesium, and iron. Life of a super red giant ends after a nuclear "burn" is roughly 10 million years and the end is marked by a supernova explosion with the heavier elements scattered in space once again. Our solar system with it abundant collection of heavier elements condensed from the gas cloud left after the explosion of a supernova. The processes within a super red giant manufactures enough oxygen so that after hydrogen and helium, oxygen with an atomic weight of eight is the third most common element in the universe. Note that carbon, the element so critical for life on earth, is also among the most abundant elements in the universe.